On the prediction of critical temperatures of ionic liquids: Model development and evaluation

In this study, the Guggenheim equation was used to estimate the critical temperature (Tc) of 106 ionic liquids using experimental surface tension data as inputs. A group contribution (GC) and a Quantitative Structure-Property Relationship (QSPR) model were also developed to correlate/predict the Tc of ionic liquids. It was shown that a lack of sufficiently large database for Tc leads to the development of models with low prediction capability. The models output as well as the Tc values estimated from the surface tension data were compared with the critical temperatures calculated by the Valderrama et al. method. The results show that the Valderrama et al. method produces different data values compared with the values calculated by the Guggenheim equation. Neither the GC, QSPR, nor Valderrama's method is capable of reliable prediction of the Tc of ionic liquids. Consequently, the calculated Tc values are not reliable enough to be used in the development of corresponding state models for prediction of other thermophysical properties of ionic liquids. Any usage of critical properties of ionic liquids should be done with a serious caution.